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ARS Home » Plains Area » Houston, Texas » Children's Nutrition Research Center » Research » Publications at this Location » Publication #163873
Title: BROWN ADIPOSE TISSUE DEVELOPMENT AND METABOLISM IN RUMINANTS

Author
item SMITH, S - TEXAS A&M UNIV
item CARSTENS, G - TEXAS A&M UNIV
item RANDEL, R - TEXAS A&M UNIV
item Mersmann, Harry
item LUNT, D - TEXAS A&M UNIV

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2003
Publication Date: 1/1/2004
Citation: SMITH, S.B., CARSTENS, G.E., RANDEL, R.D., MERSMANN, H.J., LUNT, D.K. BROWN ADIPOSE TISSUE DEVELOPMENT AND METABOLISM IN RUMINANTS. JOURNAL OF ANIMAL SCIENCE. 2004. 82:942-954.

Interpretive Summary: Brown adipose tissue (BAT) is a specialized tissue that is present in most mammals at birth. It rapidly disappears in mammals except in select rodent species where it remains throughout the lifetime and plays a major role in energy metabolism. In ruminants, BAT is present at birth and is important in thermoregulation in the newborn. The BAT is specialized in that it burns fat stored in its cells, but instead of conserving energy (like most other tissues), the energy is dissipated as heat. There is a unique protein (uncoupling protein or UCP) in the mitochondria (the energy machines of the cell) that disengages the energy storage process toward heat production. In newborn cattle, the fat in BAT cells is mostly stored as one large lipid droplet rather than many small lipid droplets (as in BAT from most species); the BAT cells do have many mitochondria. Brahman cattle do not survive as well as Angus cattle when exposed to cold. Brahman BAT had less capacity to synthesize fat stores, but had greater capacity to mobilize fat (number of adrenergic receptors) and to oxidize it for heat (UCP). Upon exposure to cold, the Brahman BAT cells shrank, whereas those from Angus did not. The data suggest that BAT from Brahman calves exhaust their lipid stores rapidly after birth to minimize heat production and decrease survival.

Technical Abstract: We conducted several experiments to better understand the relationship between brown adipose tissue (BAT) metabolism and thermogenesis. In Exp. 1, we examined perirenal (brown) and sternum s.c. adipose tissue in 14 Wagyu x Angus neonates infused with norepinephrine (NE). Perirenal adipocytes contained numerous large mitochondria with well-differentiated cristae; sternum s.c. adipocytes contained a few, small mitochondria, with poorly developed cristae. Lipogenesis from acetate was high in BAT but barely detectable in sternum s.c. adipose tissue. In Exp. 2, we compared perirenal and tailhead adipose tissues between NE-infused Angus (n=6) and Brahman (n=7) newborn calves. Brahman BAT contained two-to-three times as many total beta-receptors as Angus BAT. The mitochondrial UCP1:28S rRNA ratio was greater in Brahman BAT than in BAT from Angus calves. Lipogenesis from acetate and glucose again was high, but lipogenesis from palmitate was barely detectable. Tailhead s.c. adipose tissue from both breed types contained adipocytes with distinct brown adipocyte morphology. In Exp. 3, three fetuses of each breed type were taken at 96, 48, 24, 14, and 6 d before expected parturition, and at parturition. Lipogenesis from acetate and glucose in vitro decreased 97% during the last 96 d of gestation in both breed types, whereas the UCP1 gene expression tripled during gestation in both breed types. At birth, palmitate esterification was twice as high in Angus than in Brahman BAT and was at least 100-fold higher than in BAT from NE-infused calves from Exp. 2. Uncoupling protein-1 mRNA was readily detectable in tailhead s.c. adipose tissue in all fetal samples. In Exp. 4, male Brahman and Angus calves (n=5 to 7 per group) were assigned to 1) newborn treatment (15 h of age), 2) 48 h of warm exposure (22 degrees C) starting at 15 h of age, or 3) 48 h of cold exposure (4 degrees C) starting at 15 h of age. Brahman BAT adipocytes shrank with cold exposure, whereas Angus BAT adipocytes did not. Similarly, BAT from neonatal lambs (Exp. 5; n=6 per group) was depleted of lipid in response to cold exposure, although UCP1 gene expression persisted. In Exp. 4, NE stimulated lipogenesis from palmitate in BAT incubated in vitro. Lipogenesis from palmitate was higher in Angus than in Brahman BAT, and increased with both warm and cold exposure. These studies suggest that BAT from Brahman calves may be exhausted of lipid shortly after birth during times of cold exposure.